1. Field of the Invention
The present invention relates to a video signal multiplexer, a video signal multiplexing method, and a picture reproducer, and more particularly to a video signal multiplexer, a video signal multiplexing method, and a picture reproducer, each of which encodes picture information in a video signal to multiplex the encoded information with additional information.
2. Description of Related Art
In recent years, a technique of converting a moving image into a digital signal to record and transfer such digital data has attracted attention. In response thereto, techniques of encoding moving images such as MPEG (moving pictures expert group) are of increasing importance. Encoding the moving image is targeted at not only picture information displayed on a screen but audio information such as a voice, sound effect, and music. Further, there have been proposed a variety of multiplexing techniques for encoding additional information such as captions (subtitles) besides the picture information, and extracting the captions from the additional information to display the captions as well as the picture information at the time of reproducing the moving images (see Japanese Unexamined Patent Publication No. 2001-24983, for example).
The conventional technique of multiplexing picture information with additional information is described in brief. FIG. 9 shows a structural example of a video signal multiplexer of the related art. A video signal multiplexing apparatus 200 of FIG. 9 includes a separator 201 such as Vertical Blanking Interval DATA Slicer, an encoder 202, an encoded data storage 203, an additional information storage 204, and a multiplexer 205.
The separator 201 receives the video signal,. and separates the received video signal into picture information and additional information. In this example, the picture information refers to information about video pictures displayed on the screen in the received video signals. Further, the additional information implies other information than the picture information, but the additional information includes information such as captions and thus may be displayed on the screen after being multiplexed. The picture information and the additional information are input on a field basis. The field is a unit constituting a part of a frame.
The separator 201 separates the video signal to send the picture information to the encoder 202 and the additional information to the additional information storage 204. The encoder 202 encodes the picture information supplied from the separator 201. The data encoded with the encoder 202 is sent to the encoded data storage 203 and stored therein. The encoded data is generated for each field or frame, and recorded.
The multiplexer 205 receives the encoded data stored in the encoded data storage 203 and the additional information stored in the additional information storage 204 to multiplex these on the basis of unit group called a GOP (group of pictures). FIG. 10 shows a data flow in a multiplexing process of the related art. Additional information 10 of FIG. 10 is one stored in the additional information storage 204. Picture information frame data 20 is encoded data stored in the encoded data storage 203. The picture information frame data 20 is supplied to the multiplexer 205 on the frame basis. The multiplexer 205 receives the encoded data from the encoded data storage 203 in such amounts as correspond to the number of frames constituting the GOP. Further, the multiplexer 205 also receives the additional information 10 from the additional information storage 204 in such amounts as correspond to the number of frames constituting the GOP. The received additional information are all contained in a user data area 311 in a GOP layer 31 corresponding to a header portion of the GOP.
The multiplexer 205 creates the GOP layer 31 using the additional information supplied from the additional information storage 204 to generate GOP data 30 as stream data of each GOP with the encoded data supplied from the encoded data storage 203. Thus, the multiplexing is completed. Upon the reproduction, the encoded data is decoded into picture information to reproduce the decoded picture information, and the additional information is retrieved from the user data area 311 of the GOP layer 31 to display the resultant as caption data.
The video signal is multiplexed this way. It has now been discovered that, however, this method causes no problem as long as multiplexed data is generated in sync with the input video signal. Otherwise, a problem arises. For example, when data is encoded while converting video pictures of 24 frames/sec. such as a movie into video pictures of 30 frames/sec. such as a TV image, or when such data is decoded, synchronous signals have different time axes, so the picture rolls up or down. To prevent this, it is necessary to match phases of the synchronous signals. At this time, if the processing of separating the additional information and the picture information to match phases for the picture information is carried out as in the related art, the change in the number of frames is not reflected on the additional information, so a delay occurs during the multiplexing. Further, in the case of correcting analog signals between frames, which are liable to become unstable due to the jitter of images on a screen resulting from terrestrial waves as analog waves or unsmooth tape transport and fluctuation of the time axis, the case where the repeatedly dubbed tape is used as an input source, or other such cases, the additional information cannot be recorded normally.
Further, the synchronization can be achieved by correcting the time axis by use of a time-based corrector etc. prior to the separation. However, in this case, the corrected video signal that includes the additional information undergoes the skip or repeat processing without examining the additional information. Hence, the additional information is also partially lost due to the skip processing or is duplicated due to the repeat processing. If such additional information is multiplexed as it is, data consistency cannot be attained.
In encoding data in conformity with the MPEG standard or the like, it is necessary to consider a capacity of the user data area with a varying number of video-picture frames constituting the GOP. Howbeit, the picture information and the additional information are separately processed and thus, cannot be synchronized. Accordingly, the conventional method encounters another problem that the multiplexing is impossible with a varying number of video-picture frames constituting the GOP.
As mentioned above, the conventional technique has the problems in that the picture information is hardly synchronous with the additional information at the time of multiplexing the video signal, and in that the multiplexing is impossible with a varying number of frames constituting the GOP.